Microstructure and mechanical properties of in-situ nano γ-Al2O3p/A356 aluminum matrix composite

Abstract

In this study, the nanometer in-situ γ-Al2O3 particles reinforced aluminum matrix composites was successfully fabricated by the A356 aluminum alloy and Co3O4 powder at 850 °C by means of in-situ reaction in the high temperature melt. The effects of γ-Al2O3 particle and cobalt element on the microstructure and properties of the composites were investigated in detail. The endogenous γ-Al2O3 and cobalt could modify the coarse plate like eutectic Si into fine fibrous like and refine the second dendrite arm spacing (SDAS) of the grains simultaneously. When the content of cobalt was lower than 0.57% and content of γ-Al2O3particles was lower than 0.6 vol%, the particles distributed uniformly in the grain, however, when the particulate amount was up to 0.8 vol%, the particles would distribute at the grains boundaries or form as a rodlike phase. The grain size was sharply refined to 200 μm when the particulate content was 0.8 vol%. It was found that the ultimate tensile strength (UTS), elongation of the 0.6 vol% γ-Al2O3/A356 composites had arrived at the maximum that had enhanced by 43.6% and 85.7% in comparison to the matrix respectively, which were attributed to the homogeneous distribution of the nanoparticles, the refinement of the SDAS of the α-Al grains and the modification of the eutectic Si phases.